The present invention relates to an electric circuit breaker which automatically interrupts an electric circuit in the event of an abnormality such as an overload current or a short-circuit current. More particularly, the electric circuit breaker also automatically interrupts an electric circuit in the event of collision of a vehicle.
A general electric circuit for automobile purposes employs a fuse or a fusible link as means for immediately interrupting a circuit in case of an overload current or short-circuit current. The fuse or fusible link principally comprises a fusible conductor housed in a container and connector terminals extended to the outside of the container. Many of the fuses or fusible links are used while being connected to electric connector boxes.
Since the fuse or fusible link is originally intended to interrupt a circuit only after occurrence of an excess current, it is impossible for the fuse or fusible link to forcefully interrupt a circuit at desired timing. In the event of an emergency, such as a car accident, if forceful interruption of a circuit is desired even when there is not a flow of an excess current, it is necessary to provide the electric circuit with a circuit breaker capable of forcefully interrupting a circuit by external operation, in place of or in addition to the fuse or fusible link.
For such purposes, as described in e.g., Unexamined Japanese Utility Model Publication 56-357, an existing electric circuit breaker is configured in the following manner. Namely, a fuse ground switch is positioned between loads connected to a main fuse and a ground terminal within a circuit which supplies power to the loads from a battery via a sealed main fuse. A switch controller which turns off the fuse ground switch is positioned between the loads connected to the main fuse and the ground terminal. A collision detection sensor which activates the switch controller in the event of a collision of the vehicle is connected to the switch controller. In the event of collision of a vehicle, the fuse ground switch is turned off, thereby permitting flow of a large electric current to a sealed main fuse. The main fuse is fused, thereby interrupting supply of an electric current to vehicle loads.
Alternatively, Unexamined Japanese Patent Publication 58-47809 describes a circuit breaker of the type which forcefully breaks a conductor by utilization of blasting force of an explosive. The circuit breaker has single encapsulation glass in which an output fuse, an explosive, and a filament for heating the explosive are filled. An input terminal connected to the filament is led to the outside of the encapsulation glass so as to penetrate through the encapsulation glass. The surface of the encapsulation glass is covered with an explosion-proof film.
In such a circuit breaker, an electric current or voltage greater than a given value is applied to the input terminal in order to heat the filament, thereby blasting the explosive. The conductor can be forcefully ruptured by utilization of the blasting force of the explosive. As a result, in the event of an abnormal condition such as a short circuit in an electric circuit or an emergency condition such as a car accident, the circuit can be interrupted at desired timing by control of the electric current or voltage applied to the input terminal.
In the former electric circuit breaker described in the a foregoing publication (JP(UM) 56-357), a collision-reaction switch constituting the collision detection sensor is turned off at the time of collision of a vehicle, whereby the switch controller turns off the fuse ground switch. As a result, a large electric current commences flowing to the main fuse. Since it takes given time to fuse the main fuse since the electric current is supplied to the main fuse, the electric circuit cannot be immediately interrupted. Particularly, in order to interrupt an electric circuit by fusing a fusible link made of the main fuse, it takes long time to fuse the fusible link.
A self-hold relay constituting the switch controller prevents the circuit breaker from being erroneously operated under the influence of vehicle vibrations or prevents a contact point of the relay from being broken before the main fuse is fused. In order to cause the self-hold relay to withstand a large current supplied from the vehicle power source in the event of a short circuit in the electric circuit, a self-hold relay having a large contact capacity must be used. For this reason, the self-hold relay becomes inevitably bulky. When such a self-hold relay is mounted on a vehicle, it becomes difficult to ensure space for the relay.
In the latter circuit breaker described in the foregoing patent publication (JP 58-47809), the blasting force of the explosive is diffused in all directions within the encapsulation glass, and only a small fraction of the blasting force acts on the output fuse. For this reason, in order to ensure the rupture of a fuse, a considerable amount of blasting force as a whole is required to thoroughly break the fuse. If the blasting force is increased by an increase in the amount of explosive, there will also arise an increase in the blasting force acting on the inner surface of the encapsulation glass other than the output fuse. In order to render the encapsulation glass impervious to the increased blasting force, expensive material needs to be used for the encapsulation glass, or the glass must be subjected to special treatment, thereby entailing an increase in cost.
Furthermore, a filament constituting detonating means for exploding an explosive by heating is connected to a power source via lead wires. Upon receipt of a signal representing an abnormality; i.e., application of an electric current or voltage greater than a certain value, the filament is heated, thereby exploding the explosive. In such a configuration, if there is a flow of an electric current to the filament owing to faulty operation during the assembly of the electric circuit breaker or owing to noise due to a disturbance, there arises a risk of erroneous explosion of the explosive.